U.S. patent application number 10/807385 was filed with the patent office on 2004-11-11 for method for overdriving a liquid crystal display and defining gradation voltages therefor.
Invention is credited to Shih, Po Sheng.
Application Number | 20040222956 10/807385 |
Document ID | / |
Family ID | 33415068 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040222956 |
Kind Code |
A1 |
Shih, Po Sheng |
November 11, 2004 |
Method for overdriving a liquid crystal display and defining
gradation voltages therefor
Abstract
A method is for overdriving a liquid crystal display (LCD) and
defining gradation voltages therefor. The gradation voltages are
defined by a dynamic light transmittance vs. voltage curve. Within
a vertical scanning period, a working voltage and a black voltage
are sequentially applied to a plurality of pixels on a LCD. The
product of the applied time and the brightness curve resulting from
the working voltage is divided by the duration of the vertical
scanning period and an effective brightness is obtained from the
product operation. Moreover, the effective brightness is
transferred into an effective light transmittance. We repeat the
aforesaid steps to obtain a light transmittance vs. voltage curve,
and define a plurality of gray levels and their corresponding
gradation voltages according to the light transmittance vs. voltage
curve. The gradation voltages are relatively higher than those
defined by a steady light transmittance vs. voltage curve; and
consequently, they can accelerate the response time of the LCD.
Inventors: |
Shih, Po Sheng; (Tao-Yuan
Hsien, TW) |
Correspondence
Address: |
VOLENTINE FRANCOS, & WHITT PLLC
ONE FREEDOM SQUARE
11951 FREEDOM DRIVE SUITE 1260
RESTON
VA
20190
US
|
Family ID: |
33415068 |
Appl. No.: |
10/807385 |
Filed: |
March 24, 2004 |
Current U.S.
Class: |
345/89 |
Current CPC
Class: |
G09G 2320/0252 20130101;
G09G 2310/061 20130101; G09G 2320/0271 20130101; G09G 3/3611
20130101 |
Class at
Publication: |
345/089 |
International
Class: |
G09G 003/36 |
Foreign Application Data
Date |
Code |
Application Number |
May 11, 2003 |
CN |
092130915 |
Claims
What is claimed is:
1. A method for defining gradation voltages of a liquid crystal
display (LCD), comprising the steps of: (a) applying a working
voltage and a black voltage sequentially to a plurality of pixels
on the liquid crystal display within a vertical scanning period;
(b) integrating a brightness curve resulting from the working
voltage with time during the duration of the working voltage to
obtain a product, and deriving an effective brightness from the
quotient by dividing the product by the duration of the vertical
scanning period; (c) transferring the effective brightness into an
effective light transmittance; (d) iterating the aforesaid steps
(a)-(c) to obtain a light transmittance vs. voltage curve; and (e)
defining a plurality of gray levels and gradation voltages
corresponding to the plurality of gray levels according to the
light transmittance vs. voltage curve.
2. The method for defining gradation voltages of a liquid crystal
display of claim 1, wherein the light transmittance vs. voltage
curve expresses a dynamic relation between the light transmittance
and the gradation voltages.
3. The method for defining gradation voltages of a liquid crystal
display of claim 1, further comprising the step of: dividing the
effective brightness by the brightness of a backlight source in the
liquid crystal display to obtain the effective light
transmittance.
4. The method for defining gradation voltages of a liquid crystal
display of claim 1, wherein the liquid crystal display
simultaneously employs a black-data-insertion driving method.
5. The method for defining gradation voltages of a liquid crystal
display of claim 1, wherein each of the gradation voltages given by
step (e) is higher than each of the gradation voltages determined
by a steady light transmittance vs. voltage curve for the same gray
level so as to accelerate the response speed of the liquid crystal
display.
6. A method for overdriving a liquid crystal display, employing
gradation voltages defined by a dynamic light transmittance vs.
voltage curve, comprising the steps of: (a) applying a working
voltage and a black voltage sequentially to a plurality of pixels
on the liquid crystal display within a vertical scanning period;
(b) integrating a brightness curve resulting from the working
voltage with time during the duration of the working voltage to
obtain a product, and deriving an effective brightness from the
quotient by dividing the product by the duration of the vertical
scanning period; (c) transferring the effective brightness into an
effective light transmittance; (d) iterating the aforesaid steps
(a)-(c) to obtain a light transmittance vs. voltage curve; and (e)
defining a plurality of gray levels and gradation voltages
corresponding to the plurality of gray levels according to the
light transmittance vs. voltage curve; wherein each of the
gradation voltages is higher than each of the gradation voltages
determined by a steady light transmittance vs. voltage curve for
the same gray level so as to accelerate the response speed of the
liquid crystal display.
7. The method for overdriving a liquid crystal display of claim 6,
wherein the liquid crystal display simultaneously employs a
black-data-insertion driving method.
8. The method for overdriving a liquid crystal display of claim 6,
further comprising the step of: dividing the effective brightness
by the brightness of a backlight source in the liquid crystal
display to obtain the effective light transmittance.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for overdriving a
liquid crystal display (LCD) and defining gradation voltages
therefor, relates to an overdriving method that defines gradation
voltages by a dynamic light transmittance vs. driving voltage
curve.
[0003] 2. Description of the Related Art
[0004] The manufacturing technique for LCDs has improved in the
field of flat-panel displays with high contrast and a wide angle of
view. However, for dynamic images displaying continuous movement,
the image quality deteriorates due to a residual image phenomenon.
Recently, there have been many driving methods for improving the
image quality of LCDs, and the black data insertion method provided
by the NEC Corporation is one suitable solution for the dynamic
image issue. The prior art applies the voltage of a black datum in
a sequence to the liquid crystal (LC) capacitor of each pixel
during a frame period so as to have an "impulse-type" effect on the
same display as a cathode ray tube (CRT) does. Therefore, a user
can see sharp and clear images displaying a continuously moving
object at every instant and every angle.
[0005] FIG. 1 is the optical response waveform diagram of a
conventional LCD. The data signal 11 within each vertical scanning
period includes two potentials, a gradation voltage 111, and a
black voltage 112, wherein the black voltage 112 makes a pixel
change to black from a predetermined color in response to the
gradation voltage 111. A waveform 13 represents the delayed optical
response of an LCD, and illustrates that the light transmittance
ratio changes to zero due to the writing of the black voltage 112
before it reaches the predetermined value in terms of the gradation
voltage 111. If the function of black data insertion is removed
from the LCD, i.e., only the potential regarding the gradation
voltage 111 remains in the data signal 11, then the optical
response of the LCD is reshaped as the waveform 12 shown. The light
transmittance ratio corresponding to the peak of the waveform 12 is
designated as the default value in response to the gradation
voltage 111.
[0006] The waveform 15 shown in FIG. 1 represents the speeded
optical response of an LCD. Ordinary overdriving methods disclose
that the rapid optical response can be achieved by means of
accelerating the rotation speed of the liquid crystal molecules.
Among those methods, the dynamic capacitance compensation (DCC)
method proposed by the Korean Samsung Electronics is a practical
overdriving method. The prior art discloses that the difference of
the gradation voltages for the pixels between a proceeding frame
and a succeeding frame needs to be calculated, and appropriate
compensation voltages are given according to the difference in
value. In this way, the optical response of the pixels is
accelerated. However, the prior art cannot be applied to the LCD
together with the driving method of black data insertion, because
if a black voltage 112, which makes the pixel turn black, is
applied to each of the pixels between two adjacent frames, the
compensation voltages, which is still determined by the gradation
difference between the two frames, certainly causes the pixels not
to display adequate gray levels during the next frame.
[0007] Usually, the gradation voltage corresponding to the light
transmittance is obtained by a steady transmittance vs. voltage
(T-V) curve, as shown in FIG. 2. If a voltage is applied to the two
terminals of the liquid crystal capacitor of a pixel, the liquid
crystal molecules in the liquid crystal capacitor are rotated to a
predetermined angular posture due to the change of the electric
field, and meanwhile the light transmittance measured for the pixel
is designated as a steady light transmittance after the posture of
crystal liquid molecules remain steady. Referring to FIG. 2,
T.sub.L0-T.sub.L255 are the light transmittances corresponding to
each gray level of a eight-bits data signal (L0-L255 have 256
levels in all), and the corresponding gradation voltages
V.sub.L0-V.sub.L255 for driving the liquid crystal capacitor can be
obtained respectively according to the T-V curve.
[0008] However, the brightness felt by human retinas is not a
constant value in a steady state, but it is the effect based on the
product of the variable brightness and the sensing time. Usually,
the brightness of the LCD is obtained by the light transmittance
multiplied by the brightness of a backlight source having a
constant brightness in general. Therefore, even if the prior art
has taught us to accelerate the response speed of the liquid
crystal capacitor, it still cannot satisfy the time factor of the
brightness felt by the viewer's vision because of the existence of
the delay phenomenon in the optical response.
SUMMARY OF THE INVENTION
[0009] The objective of the present invention is to provide a
method for overdriving a liquid crystal display and defining
gradation voltages therefor. The method discloses that a dynamic
light transmittance vs. voltage curve is derived from the product
of variable brightness and time. The gradation voltage
corresponding to each gray level can also be defined by means of
the dynamic relation curve, therefore it can satisfy the time
factor of the brightness felt by the viewer's vision because of the
existence of the delay phenomenon in the optical response.
[0010] In order to achieve the objective, the presented invention
discloses a method for overdriving the liquid crystal display (LCD)
and defining gradation voltages therefor. The gradation voltages
are defined by a dynamic light transmittance vs. voltage curve.
Within a vertical scanning period, sequentially a working voltage
and a black voltage are applied to a plurality of pixels on a LCD.
And the product of the applied time and the brightness curve
resulting from the working voltage is divided by the duration of
the vertical scanning period and an effective brightness is
obtained from the product operation. Moreover, the effective
brightness is transferred into an effective light transmittance. We
repeat the aforesaid steps to obtain a light transmittance vs.
voltage curve, and define a plurality of gray levels and their
corresponding gradation voltages according to the light
transmittance vs. voltage curve. The gradation voltages are
relatively higher than those defined by a steady light
transmittance vs. voltage curve; consequently, they can accelerate
the response time of the LCD.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention will be described according to the appended
drawings in which:
[0012] FIG. 1 is an optical response waveform diagram of a
conventional LCD;
[0013] FIG. 2 is a graph of a conventional light transmittance vs.
voltage curve;
[0014] FIG. 3 is a graph of a brightness curve in accordance with
the present invention;
[0015] FIG. 4 is a graph of a light transmittance vs. voltage curve
in accordance with the present invention; and
[0016] FIG. 5 is a graph of an effective brightness vs. voltage
curve in accordance with the present invention
PREFERRED EMBODIMENT OF THE PRESENT INVENTION
[0017] In order to speed up the optical response of an LCD, the
present invention provides an overdriving method for the LCD, i.e.,
it achieves the acceleration and brightening effects by increasing
the driving voltage. FIG. 3 is an illustrative graph of a
brightness curve in accordance with the present invention. Curves
31, 32 and 33 respectively represents the variations of brightness
along a time axis and are obtained from respectively applying
working voltages V.sub.1, V.sub.2 and V.sub.3 to the two terminals
of the liquid crystal capacitor of a pixel during a t, interval.
The three curves are also expressed by the brightness functions
B.sub.1 (t), B.sub.v2 (t) and B.sub.v3 (t).
[0018] When time is at the ti moment, a black voltage is instantly
applied to the pixel for reducing the brightness towards zero. When
time is at the t.sub.2 moment, a complete vertical scanning period
ends. We integrate the brightness functions B.sub.v1 (t), B.sub.v2
(t) and B.sub.v3 (t) by time within the vertical scanning period to
obtain their corresponding brightness accumulation, and the
brightness accumulation is divided by the vertical scanning period
t.sub.0-t.sub.2 to obtain their corresponding effective brightness
respectively as the following formulas express: 1 B V1 ' = 1 t 2 -
t 0 t 0 t 2 B V1 ( t ) t ; B V2 ' = 1 t 2 - t 0 t 0 t 2 B V2 ( t )
t ; and B V3 ' = 1 t 2 - t 0 t 0 t 2 B V3 ( t ) t ;
[0019] wherein B.sub.V1.sup.', B.sub.V2.sup.' and B.sub.V3.sup.'
are the effective brightness corresponding to the working voltages
V.sub.1, V.sub.2 and V.sub.3, respectively.
[0020] As shown in FIG. 2 and FIG. 3, the steady state value of the
brightness curves 31, 32 and 33 are almost equal to each other,
that is, B.sub.V1 (t.sub.1).apprxeq.BV2 (t.sub.1).apprxeq.B.sub.V3
(t.sub.1). In other words, after applying working voltages V.sub.1,
V.sub.2 and V.sub.3 to the two terminals of the liquid crystal
capacitor of a pixel during an interval, respectively, the liquid
crystal molecules in the liquid crystal capacitor are rotated to a
predetermined angular posture due to the change of the electric
field, and meanwhile the light transmittance measured for the pixel
is approximately the same for these applied working voltages. But
apparently the areas of three shadow portions in this figure are
quite different; therefore the effective brightness,
B.sub.V1.sup.', B.sub.V2.sup.' and B.sub.V3.sup.', corresponding to
the working voltages, V.sub.1, V.sub.2 and V.sub.3, are different
from each other.
[0021] By iterating the aforesaid steps, other applied voltages and
their corresponding effective brightness also can be obtained, and
meanwhile an effective brightness vs. voltage curve can be depicted
from this data, as shown in FIG. 5.
[0022] FIG. 5 is a graph of an effective brightness vs. voltage
curve in accordance with the present invention. An effective light
transmittance T.sub.VX.sup.' can be derived from the effective
brightness B.sub.VX.sup.' divided by the brightness of a backlight
as follows: 2 T VX ' = B VX ' L ;
[0023] wherein V.sub.X represents the working voltage corresponding
to the effective brightness B.sub.VX.sup.' and L represents the
brightness of the background light source.
[0024] Therefore, the effective brightness vs. voltage curve in
FIG. 5 can be transferred into the effective light transmittance
vs. voltage curve in FIG. 4. We define the gray levels and its
corresponding gradation voltages according to the dynamic light
transmittance vs. voltage curve in FIG. 4. Hereinafter, an LCD with
eight-bits data signal provided is regarded as the embodiment of
the present invention; therefore, the determined gray levels of a
pixel totally have 256 levels ranging from L.sub.0 to L.sub.255. In
comparison with the prior art in FIG. 2, gradation voltages
V.sub.1.255.sup.D.multidot.V.sub.1.254.sup.D and VD.sub.1.253.sup.D
are defined by the method of the present invention, and their
inequalities are obtained as follows:
V.sub.1.255.sup.D>V.sub.1.255;
V.sub.1.254.sup.D>V.sub.1.254; and
V.sub.1.253.sup.D>V.sub.1.253.
[0025] That is, the gradation voltages for driving the liquid
crystal capacitor are relatively increased so as to accelerate the
optical response of the LCD.
[0026] Apparently, the dynamic effective brightness vs. voltage
curve is derived from the product of the variation of brightness
and time, and the objective of the present invention is to meet the
time effect of the brightness felt by viewer's vision. On the other
hand, the duration of the optical response for the LCD is shortened
by the increase of the driving voltage, and meanwhile the
brightness displayed by each frame is also raised.
[0027] The above-described embodiments of the present invention are
intended to be illustrative only. Numerous alternative embodiments
may be devised by persons skilled in the art without departing from
the scope of the following claims.
* * * * *